Transformers - The original was a fresh, exciting, funny and engaging "boy and his dog" film for the new century. Drunk with power Michael Bay then used the subsequent installments to prove he hates everyone not named Micheal Bay and in the process tarnished Executive Producer Steve Spielberg's previously sparkling reputation.
Batman Begins - This gritty, life-sized portrayal of Batman's origin was followed by two of the worst comic book movies ever made. The Dark Knight was a dreadfully dull affair set in a boring, empty city where the director gave Christian Bale free reign to indulge his pretensions. While TDKR confirmed once and for all what TDK powerfully suggested: that Nolan has no idea what to do with a big budget. (As if any more proof were needed see Inception and Interstellar)
The Matrix - Of course the original was released in 1999 but II and III were 21st century fiascos of epic proportions. Another case of big budget-itis this time with the Wachowskis instead of Nolan doing the deer-in-headlights imitation. Each film had the unmistakable air of being made up as it went along by people with very little imagination who were still trying to fathom how they could have got so lucky. Good question indeed.
The Bourne Identity - In spite of Matt Damon the first movie succeeded in demonstrating the untapped potential of the spy thriller. The sequels did little to build on that potential. All they really accomplished was to point out that the main character isn't smart enough to buy some sunglasses or wear a hat and that the 'actor' portraying him has the dramatic range of a turnip. Oh yeah, and how about that editing. Pretty radical.
The Hangover - The sequels were nasty, pointless affairs that rested firmly on the hope that celebrity would trump quality and put consumer butts in theater seats. To a degree that hope was validated.